I've had to do this several times to build shelves etc. Try to cut a board that will fit nicely against the totally irregular curve of the hull. I need to do it once again, and am wondering if anyone out there has any tips to make this easier.

How do I map the curvature onto a board which I can then cut to shape?

You can also eye ball it cut the cardboard semi close...then cut a bunch of smaller pieces of thin stuff like poster board (or even paper if your close enough), sliding them over the main piece until they touch the shape then tape them down....one after the other..like a dashed line.....lots of time can be wasted trying to make the template from just one piece....it can be a hundred pieces taped together.

How complex is the curve?
Like a lot of these guys are saying you need a template and for complex shapes get 1/8" door skin at Home Depot, rip it into 2" wide strips, cut these strips into lengths short enough to work with individually that you can scribe as sections and while they are in position use hot melt glue to fasten the adjacent pieces together. If the template gets too large or cumbersome make it as 2 or 3 sections that are labeled to reassemble at your work area.

I had to repair part of the counter top on Espie, as it had rotted out. The PO had cut away the bad material, and left an odd shape. A parallelogram with one long side curved to match the hull.

I took my carpenters square, and drew a line at 90 deg to the aft bulkhead, and then drew a series of lines parallel to the aft bulkhead spaced 2 inche apart. Then I just measured the offsets at each parallel, recorded them and transferred them to the plywood. Cut it out with the band saw and did a trial fit. Took off a couple of high points with my angle grinder and a sanding disk. I then went along the entire hull side edge and beveled it to fit. Drop in piece fitted perfectly.

I've found the best way to make shelving is to use thin wood strips tacked together with a hot melt glue gun. Scribe the curve as others have said, then remove the one assembly you've glued together and trace to a board.

How complex is the curve?
Like a lot of these guys are saying you need a template and for complex shapes get 1/8" door skin at Home Depot, rip it into 2" wide strips, cut these strips into lengths short enough to work with individually that you can scribe as sections and while they are in position use hot melt glue to fasten the adjacent pieces together. If the template gets too large or cumbersome make it as 2 or 3 sections that are labeled to reassemble at your work area.